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EVM vs. PER Plot: Importance of Signal Quality Measures in Wireless Communication

Explore the comparison between Error Vector Magnitude (EVM) and Packet Error Rate (PER) in assessing signal quality for wireless communication systems, as discussed by Brian Hart and David Skellern from Cisco Systems. The study evaluates the relationship between EVM and PER across various channels and practical implementations, highlighting the limitations and potential extensions of EVM as a signal quality metric. The investigation, presented in the context of IEEE 802.11 standards, aims to provide insights into the effectiveness of existing measures and the need for standardized metrics in evaluating communication link performance.

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EVM vs. PER Plot: Importance of Signal Quality Measures in Wireless Communication

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  1. EVM vs PER Plot Not Promising for PSNI Brian Hart, David Skellern (Cisco Systems) skellern@cisco.com, brianh@cisco.com TGk July 2003 Hart/Skellern Cisco

  2. Background • IEEE 802.11-03/218r2 (file 11-03-218r2-K-PSNI_Measurement_V2.ppt) proposed the use of a measure named PSNI to quantify the quality of the signal that is able to be recovered by a particular receiver • In document IEEE 802.11-03/531r0 we suggested that a new measure was not needed because an appropriate measurement of output signal quality was already available in EVM which: • works for all digital modulations • has the desired properties specified on slides 9 & 10 of doc: IEEE 802.11-03/218r2 • can provide a direct indication of observed S/(N+I) considering all channel impairments and implementation losses when measured at the demodulator • is defined already in the standard as a signal quality measure • can be measured with commercially available test equipment Hart/Skellern Cisco

  3. Background cont. • However, discussion in TGk at the May 2003 concluded that • Simulations and/or measurements were needed to verify the validity of EVM as an output signal quality measure • Even if EVM was a valid measure, it was a measure that needed to be extended to take into account the implementation characteristics of the receiver from the demodulator to the output (principally the FEC block) • This submission is about the validity of EVM and reports on an investigation of the relationship between EVM and PER across different channels and practical systems. Hart/Skellern Cisco

  4. Investigation of EVM validity • We thought that if any useful standardized PSNI measure existed it would be based on EVM because it captures all the degradations present on a communications link • in proportion to the impact they have • at a point where the cumulative degradation is easy to estimate • includes: quantisation, non-ideal converters, clock frequency offsets and phase noise, carrier frequency offsets and phase noise, power-amplifier distortions, multipath, co-channel interference, adjacent channel interference, other interference, thermal noise, and poor receiver algorithms. • We therefore expected that if we plotted average EVM vs average PER for an IEEE 802.11a link operating at a given rate over a range of practical implementations and typical channels we would find a useful relationship between EVM and PER. Hart/Skellern Cisco

  5. Investigation of EVM validity • We generated results using a Matlab 802.11a modeling framework • with a range of channels, from AWGN to Rayleigh, that we believe from our channel measurements to be representative of the indoor office environment • with a range of practical hardware settings and implementations, including ADC resolutions, datapath widths, Viterbi algorithm details, synchronization options, channel tracking methods and AGC strategies “practical hardware settings and implementations” = workable designs, many of which are in current manufacturers’ implementations • Simulation set-up • there are over 250 plotted simulation points • generally the simulations wait for 75 1000-byte packets in error or 750 packets, whichever comes first • a few points (<< 5%) at high PER are based on fewer packets Hart/Skellern Cisco

  6. EVM vs PER results for 6 Mbit/s Genie-aided EVM is EVM calculated using the known transmitted constellation point. Hart/Skellern Cisco

  7. Conclusion • These results show no useful relationship between EVM and PER across different channels and practical systems. • While further study is needed, we conclude that obtaining an output data quality measure that would be useful across different designs and implementations (manufacturers) is unlikely in the short term – and not in any timeframe commensurate with timely completion of an 11k draft. • We therefore propose that text related to PSNI not be included in the draft. Hart/Skellern Cisco

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